The present invention relates to drilling and completion techniques for downhole wells, and more particularly, but not exclusively, to drillable, anti-rotation devices for use with plugs, float collars and float shoes.
The process of drilling subterranean wells to recover oil and gas from reservoirs, consists of boring a hole in the earth down to the petroleum accumulation and installing a pipe liner from the reservoir to the surface. Casing is the protective pipe liner within the wellbore that is cemented in place to prevent collapse of borehole walls and to insure a pressure-tight connection from the surface to the oil and gas reservoir. Casing is typically run into the hole in sections, one section at a time and then is cemented in place. Drilling may then be continued below the casing until the reservoir is reached.
Typically, primary cementing is performed by running in a steel, non-drillable casing string into the wellbore. The casing string commonly has a float collar positioned one or two joints above the float shoe which is at its lower end. Collars and shoes help prevent the back flow of cement during cementing operations. The collars and shoes are usually equipped with a check-valve to prevent cement from returning up the interior of the casing string. Once the casing is run to the desired depth, the casing remains filled with drilling fluid and the cementing operation may begin.
When it is desired to cement the casing in the wellbore, a bottom plug or wiper plug is launched in the casing between the fluid in the well and the cement slurry. This bottom plug commonly has a fluid passage through it which may be sealed by a diaphragm or membrane. The cement is pumped into the casing on top of the bottom plug, forcing the bottom plug down the well, displacing the mud below the plug out of the well, until the bottom plug seats on the float collar, or shoe, or a shoulder. Once the plug reaches the restriction, pumping pressure is increased. This ruptures the seal in the plug""s fluid passage and the cement slurry flows through the plug and through the fluid passage of the shoe or collar. Once the required amount of cement is pumped into the well, a top plug is launched into the casing atop the fluid cement column. Typically, the top plug does not have a fluid passage through it. A fluid such as mud or drilling fluid is then pumped into the casing, forcing the top plug and the fluid cement column down the hole and up into the annulus between the casing and the wellbore. It should be recognized that one or more top or bottom plugs may be utilized in cementing operations.
The plugs are usually constructed of a pliable or elastomeric material, such as plastic, wood, rubber, or aluminum, and commonly have a hollow metal or plastic core. The plugs traditionally also have wiper wings which fit snugly within the steel, non-drillable casing string. All of the plugs are constructed of a drillable material. The plugs have three primary purposes: (1) to separate the wet cement slurry from the fluid it is displacing or the fluid which is being used to pump the cement slurry to the desired level; (2) to wipe off the inner surface of the pipe string as the plug travels down the hole; and (3) to aid in preventing back flow of the cement pumped into the casing/hole annulus as the cement sets.
Once the cement has set up and other desired operations have been performed, the plug(s), collar, shoes, and cement may be drilled out. In order to drill the well out, the drill string is run back into the hole until the drill contacts the top plug and the string and drill bit are rotated. In all too many instances, when the drill bit is rotated the plug and set cement within or about it begins to rotate atop of the plug, cement, collar, or shoe on which it rests. This rotation of the plug wastes valuable time and energy in attempting to drill out the well.
Attempts in the past have been made to prevent the rotation of the plug(s) and associated set cement to aid in the drilling of the plugs. One device is disclosed in U.S. Pat. No. 5,842,517 and assigned to Davis-Lynch, Inc. The ""517 patent discloses a combination float collar, cement plug, and wiper plug each having inclined J-slots for interconnecting the pieces.
U.S. Pat. No. 5,390,736 assigned to Weatherford/Lamb, Inc., discloses interconnectable plugs and float collars having a xe2x80x9cbuntxe2x80x9d design. The ""736 teaches forming a male xe2x80x9cbuntxe2x80x9d shaped end and female xe2x80x9cbuntxe2x80x9d end for fitting the male end.
U.S. Pat. No. 5,165,474 assigned to Dowell Schlumberger, discloses an anti-rotation device for plugs having deformable lips. The ""474 teaches a tubular section having a high coefficient of friction, a divergent internal diameter, and a plurality of horizontal annular teeth opposing axial movement of the cement plug within the casing string.
U.S. Pat. No. 5,095,980 assigned to Halliburton Company, discloses a combination non-rotating plug set. The ""980 patent teaches a combination of plugs and a collar having molded inserts or teeth. The teeth are adapted to interconnect when the individual tools are in contact to prevent rotation of the interconnected pieces.
U.S. Pat. No. 4,190,111 to Davis discloses an anti-rotation tool to be used in combination with a plug. The ""111 teaches a flat plate having protrusions on both faces of the plate. The protrusions are designed to engage, dent and penetrate a cement surface on the plug. The plate is run below the wiper plug.
To date these prior art anti-rotation devices have failed to consistently and effectively prevent the rotation of the plugs when drilling out. In many cases at least one if not all the engaging surfaces fail to engage, allowing rotation of the plugs. In addition, it is not uncommon to fail to pump the plugs in contact with one another, preventing interconnection of the plugs. Further, in deviated or horizontal wells it is difficult, at best, to interconnect the tools to be drilled out, thereby resulting in failure to limit rotation of the plug. Additionally, it is common for the teeth, slots, hooks, protrusions to slip or fail negating the purpose of the devices. Further, the prior art devices require the purchase of interconnecting pieces, such as, a set of plugs and a corresponding shoe or collar from the same vendor, thereby limiting the choice of an operator to select preferred plugs, collars, and shoes.
It would be a benefit therefor, to have an anti-rotation device which is reliable and inexpensive. It would be a further benefit to have an anti-rotation device which does not require interconnection of the plugs to prevent rotation. It would be a still further benefit which does not require interconnection between the plugs and shoe or collar. It would be an additionally benefit to have an anti-rotation device which is adapted for use in deviated and horizontal wells. It would be a still further benefit to have an anti-rotation device which may be used with collars, shoes, and plugs originating from differing sources.
The present invention is an anti-rotational device of the type used for limiting the rotation of plugs and tools when being drilled out. The anti-rotational device includes: a drillable, substantially cylindrical sleeve connectable within a substantially undrillable pipe string, in the preferred embodiment, a steel, non-drillable string of cylindrical oilfield casing. As used herein, xe2x80x9csubstantially cylindricalxe2x80x9d is intended to cover a sleeve which not only is truly cylindrical, but also a sleeve which is at least partially tapered from one of its ends to the other. The sleeve has at least one rib or discontinuous sets of ribs or other sets of protrusions or grooves or other sets of indentations formed within the interior of the sleeve. The sleeve is formed to dispose at least one plug therein limiting the rotation of the plug and associated set cement when drilling out.
The drillable sleeve is a tubular member forming a passageway therethrough. The sleeve may be formed of any type of drillable material such as pliable rubbers and plastics, wood, aluminum, brass and the like. Many of these materials are currently used in drillable tools such as the plugs, wipers, float shoes or collars or the like. Formed along the interior surface of the sleeve are protrusions such as ribs. These ribs may be formed substantially along or discontinuously along the longitudinal axis of the sleeve, or they may be formed in a substantially circumferential non horizontal pattern, or at an acute angle with respect to the longitudinal axis of the drillable sleeve. In the substantially longitudinal projection the ribs or other protrusions act as a brake or high frictional engaging force against the rotation of the plugs. In a slanted or helically xe2x80x9cthreadedxe2x80x9d configuration, the ribs or other protrusions can be arranged so as to counteract the downward force and rotation of the drill bit and string and tend to force the plug upwardly against the bit, and counter to the rotation of the bit thereby aiding in the drilling of the plug. Such a configuration can substantially thread the plug or tool down to the bottom of the float collar or shoe to aide in drilling the plugs or other tools out. The rib(s) or other protrusions or grooves may have a substantially semi-circular, pseudo-circular, rectangular, triangular, or other profile which will aide in gripping the plugs and preventing rotation of the plugs or other tools. The formed passageway of the present anti-rotational device may be cylindrical or tapered from top to bottom at a small angle to assist in preventing longitudinal motion of the plug and associated set cement while it is being drilled.
The sleeve may be formed by molding within a piece of material such as collar stock, a pup joint, casing joint or other material. Additionally, the sleeve may be formed so as to be insertable into material available at the well site, such as a joint of steel casing. In this instance the sleeve can be snugly adhered to the interior of the casing, from one end of the sleeve to the other, using commonly known adhesives such as well cement. In other words, the entire length of the sleeve is preferably right up against the interior surface of the casing, other than for any adhesive material between the sleeve and the casing. Additionally, the sleeve may have threads formed on the exterior thereof for threading into a housing or outer member such as casing or collar stock. This second embodiment more readily allows the anti-rotational device be adjusted to conditions and situations which may be encountered on-site.
The sleeve, whether molded or inserted into a member, may be connected directly to a float collar, shoe, or within a joint not directly adjacent to the shoe or collar. Examples of the anti-rotation device are: a pup joint for connecting where desired; an inline centralizer having an anti-rotation device; a float collar having the anti-rotation device formed therefrom or therein; a float shoe having the anti-rotation device formed therefrom or therein; various length pup joints for multiple plugs; and the sleeve anti-rotational device being formed as an insert which for example may be threaded into or adhered in a conduit such as collar stock or a joint of pipe or casing. It should be recognized that the anti-rotation device can be made and altered on-site to accommodate various desired lengths such as for one plug, two plugs, or multiple plug operations. Additionally, the anti-rotation device of the present invention may be used with plugs manufactured by one vendor and shoes and collars manufactured by another vendor.
In an alternative method, the anti-rotation device may be disposed within the casing string well away from a shoe or collar to provide an indication of the location of a plug as it is being pumped down hole. The location can be determined from the spike in pump pressure when the plug encounters and passes through the anti-rotation device.
In use the anti-rotation device is placed in the steel casing string, typically by threading the substantially nondrillable outer member containing the sleeve into the pipe string. The operator may choose whether the anti-rotation device be pre-molded in a carrier or as an insert depending on the location. Additionally, the length of the anti-rotation device may be preselected or adjusted by selecting pups or interconnecting pieces. The inside diameter of the anti-rotation device is selected so that when drilled out, the inside diameter of the non-drillable casing string remains substantially the same as that of the adjacent pipe string. The anti-rotation ribs or protrusions extend inwardly within the interior of the sleeve so as to compress a portion of the wings or lips of the plug. The wings may be deflected approximate their maximum deflection limits which is disclosed in plug vendor""s specifications. The invention contemplates using one or more grooves or other indentations instead of using protrusions, and also contemplates the use of grooves or other indentations in combination with protrusions to prevent the cement plug from rotating.
When the plug is launched into the casing string it is forced down hole by a fluid such as drilling mud or cement. When it reaches the anti-rotation device of the present invention the circumferential wings of the plug are deflected by the ribs of the sleeve lodging the plug within the sleeve. When the grooves are used within the anti-rotation device of the present invention, the elastomeric portion or portions of the cement plug are forced into one or more grooves by the weight of the drill bit, which aids in causing the cement plug not to rotate within the device. It is necessary, in particular for the bottom plug, that the force and pressure necessary to lodge the plug into the anti-rotation device is not so great as to rupture the sealed fluid passage way. In addition, if more than one rib is formed along the interior of the sleeve the ribs are spaced at a distance such that the plug""s wings substantially form a seal against the interior of the sleeve to limit back flow of fluid and in particular cement slurry.
If it is desired, a second, third or more plugs are run into the hole as is well known in the art and lodged into the anti-rotation device. It is not necessary that each of the plugs interconnect with each other or with the collar or shoe. The lack of necessity for the plugs or plug and collar or shoe to interconnect is especially beneficial in deviated or horizontal wells.
When it is desired to drill out the plugs, collar, shoe, and cement, the drill bit is run into the hole on the drill string. When the top plug is encountered, the bit is rotated traditionally to the right to cut up and destroy the drillable obstructions within the non-drillable casing. As the bit rotates the plugs tend to follow the rotation of the bit, resulting in failure to drill out the plugs or increased time and energy to drill out the plugs. However, contrary to the methods and apparatus which have been known in the prior art, with the anti-rotation device of the present invention the sleeve ribs or other protrusions and/or grooves or other indentations within grip the plug and associated set cement and limit the rotation of the plug allowing it to be drilled out. In a preferred embodiment, the ribs have a semi-circular or quarter-circular profile with the planar side disposed against the direction of rotation of the plug during drill out. This design provides gripping strength to the ribs and lateral strength to withstand the rotational forces. Additional embodiments, such as a triangular profile also provide strength against the rotational force. Additionally, as cement is pumped through the cement plug it sets up in the annulus formed between the deflected portion of the wings and the sleeve ribs, thereby providing additional anti-rotation forces at least against rotation of the cement plug and the wiper plug.